By using decode function, count mismatch between source and target

Question

Source query:
select distinct
frm_track_id,
--ATTRIBUTE_NAME,
SUBSTR(ATTRIBUTE_NAME,INSTR(ATTRIBUTE_NAME,'_',1,1)+1,INSTR(ATTRIBUTE_NAME,'_',1,2) - (INSTR(ATTRIBUTE_NAME,'_',1,1)+1)) LOCUS,
frm_id,
frm_maj_version,
--'null' as ETL_LOAD_STATUS,
--'null' as ETL_LOAD_DTE,
--'null'as ETL_LOAD_STATUS2,
DECODE(attribute_name,( select attribute_name from dual where attribute_name like '%_allele1'), OUTPUT_ANSWER_VAL, null) ORIGINAL_LOC_ALLELE1
--DECODE(attribute_name, (select attribute_name from dual where attribute_name like '%_allele2'), OUTPUT_ANSWER_VAL, null) ORIGINAL_LOC_ALLELE2,
--DECODE(attribute_name, (select attribute_name from dual where attribute_name like '%_ser1'), OUTPUT_ANSWER_VAL, null) ORIGINAL_LOC_SER1,
--DECODE(attribute_name, (select attribute_name from dual where attribute_name like '%_ser2'), OUTPUT_ANSWER_VAL, null) ORIGINAL_LOC_SER
from iidb_stg.stage_fn_base_translate
where attribute_name in ( 
'loc_a_allele1','loc_a_allele2','loc_a_ser1','loc_a_ser2', 
'loc_b_allele1','loc_b_allele2','loc_b_ser1','loc_b_ser2', 
'loc_c_allele1','loc_c_allele2','loc_c_ser1','loc_c_ser2', 
'loc_dp_ser1','loc_dp_ser2', 
'loc_dpa1_allele1','loc_dpa1_allele2', 
'loc_dpb1_allele1','loc_dpb1_allele2', 
'loc_dq_ser1','loc_dq_ser2', 
'loc_dqa1_allele1','loc_dqa1_allele2', 
'loc_dqb1_allele1','loc_dqb1_allele2', 
'loc_dr_ser1','loc_dr_ser2', 
'loc_drb1_allele1','loc_drb1_allele2', 
'loc_drb3_allele1','loc_drb3_allele2', 
'loc_drb4_allele1','loc_drb4_allele2', 
'loc_drb5_allele1','loc_drb5_allele2' 
and frm_track_id=308678
order by 1,2
result set:
frm_track_id
LOCUS
frm_id
frm_maj_version
ORIGINAL_LOC_ALLELE1
308678
a
2005
1
205
308678
b
2005
1
3502
308678
c
2005
1
401
308678
dqb1
2005
1
301
308678
dqb1
2005
1
null
308678
drb1
2005
1
403
308678
drb1
2005
1
null
Target Query:
select distinct
FRM_TRACK_ID,
LOCUS,
FRM_ID,
FRM_MAJ_VERSION,
--ETL_LOAD_STATUS,
--ETL_LOAD_DTE,
--ETL_LOAD_ID,
--ETL_LOAD_STATUS2,
ORIGINAL_LOC_ALLELE1
--ORIGINAL_LOC_ALLELE2,
--ORIGINAL_LOC_SER1,
--ORIGINAL_LOC_SER2
from
IIDB_STG.OPS_FN_SBJCT_TYPING
where FRM_TRACK_ID=308678
order by 1,2
result set:
frm_track_id
LOCUS
frm_id
frm_maj_version
ORIGINAL_LOC_ALLELE1
308678
a
2005
1
205
308678
b
2005
1
3502
308678
c
2005
1
401
308678
dqb1
2005
1
null
308678
drb1
2005
1
403

Answer 1

In Source, you are selecting from  iidb_stg.stage_fn_base_translate, however in target query you are selecting from IIDB_STG.OPS_FN_SBJCT_TYPING. the only condition in both where clause is of FRM_TRACK_ID=308678, so i assume that the missing 2 records are not present in
IIDB_STG.OPS_FN_SBJCT_TYPING table. Modifying the target query might not resolve issue but you have to check why these two records are missing from this table in first place.